The present invention relates to a lift or transfer pump for supplying fuel from a tank to an internal combustion engine. More particularly, the invention relates to a device and method to prevent dry running of a lift pump.
Internal combustion engine powered devices typically include a lift pump to transfer fuel from a remote tank to the engine fuel supply. The engine fuel supply may comprise a carburetor, a fuel injection system, or a high pressure fuel injection pump. While lift pumps may be mechanically driven, electric motor powered lift pumps have become common place. These electric powered lift pumps are energized to operate whenever the engine electrical system is in a start or run condition. The lift pump, or a downstream portion of the fuel system, will include a pressure switch or a pressure regulator and return line to prevent "dead heading" of the lift pump. Thus, it is possible for the fuel pump to continue operating when the ignition is in the on condition but the engine is not operating.
The ability of the lift pump to operate when the engine is not also operating leads to a number of potential problems. In the case of an ignition switch inadvertently left in the on position with the engine not operating, the lift pump will operate and drain the battery. Further, continuous operation of the lift pump circulates fuel through the fuel system and back to the tank leading to fuel heating. More seriously, if the fuel tank empties so that the lift pump runs dry, the continuously operating lift pump motor can overheat. In severe cases of dry running, the motor commutator melts, requiring costly and time consuming replacement of the lift pump before the vehicle can be restarted.